Electron discharge device



Dec. 10, 1946. o,- H.-SCHADE 2,412,291

ELECTRON. DISCHARGE DEVICE Filed May 30, 1942 3 Sheets-Sheet 1 JAllAAAIMIEOF E0707? 3nocntor 3 Sheets-Sheet 2 Filed ma 30, 1942 Dec. 10, 1946.v o. H. SCHADE ELECTRON DISCHARGE DEVICE 3 Shee ts-Sheet 3 Filed May 30,1942 Snventor attorney Patented Dec. 10, 194$ "E E S in T 2,412,291ELECTRON mscnAnoE nEvrcE of Delaware Application May 30. 1942, SerialNo. 445,185

8 Claims. (01. 315-44) This invention relates to deflection circuits forcathode ray indicating systems, and more particularly to circuits forproducing linear radial traces on the fluorescent screen of a cathoderay tube. The words radial trace are used to refer to a trace having oneof its ends at or near the center of the cathode ray tube screen, asdistinguished from a diametral trace, having its ends approximatelyequidistant from the center of the screen. In certain applications ofcathode ray tubes, as in some types of radio distance and directionindicators, it is desirable to produce a radial trace which is rotatableabout its inner end to correspond in direction with the angular positionof a remote shaft, which, for example, may be connected to a rotatabledirectional antenna. The problem is complicated by the fact that theremote control shaft need not necessarily rotate at a constant speed,but may be stopped and reversed. a

The conventional deflection means in a cathode ray tube is a stationaryfour-pole system consisting of four rectangularly disppsed deflectionplates for electrostatic deflection or two pairs of deflection coilsarranged at right angles for magnetic deflection. According to thisinvention, the line of deflection of the beam in a cathode ray tube isrotated about one of its ends at the axis of the tube by impressing uponeach of the beam deflecting means a sawtooth wave or other sweep signalof sinusoidally varying amplitude. The sinusoidal variations on one pairof the beam deflecting means differ in phase by 90 from the variationson the other pair.

The principal object of this invention is to provide an improved methodof and means for deflecting a cathode ray beam. Another object of thisinvention is to provide improved means for generating signals for radialdeflection of a cathode ray beam, said signals being controlled inamplitude in accordance with the angular position of the rotor of aremote control unit so as to produce a synchronous angular displacementof the radial cathode ray beam trace. A further object is to provide animproved system of the described type in which the length of the radialtrace is constant throughout a 360 rotation independent of the speed ofrotation. Other objects, features and advantages of this invention willbe apparent to those "skilled in the art upon consideration of thefollowing specification with reference to the accompanying drawings, inwhich Figs. 1 and 2 are graphs representing the wave forms of voltagesor currents required in electrostatic or magnetic .deflection systemsrespectively to produce rotation of a unidirectional deflecting field;Fig. 3 is a circuit diagram showing one form of this invention; Figs.4a, 4b, 4c, 4d, 4e and Figs. 5a, 5b, 5c, 5d, 5e, 5), 5g and 5h aregraphs representing wave forms of voltages produced in operation of thedevice of the invention; Figs. 6, '7, 8, 9 and .10 are schematicdiagrams of modified deflection voltage amplifier and D.-C. insertioncircuits; Fig. 11 is a diagram of a circuit for the use of modulatedsine wave, instead of sawtooth, deflecting voltages; Figs. 12a and 12bare graphs of wave forms illustrating sawtooth wave distortion and itscompensation; and Figs. 13a, 13b and 130 are graphs of three sawtoothwaves having the same amplitude and repetition time but differentslopes.

Referring to Fig. 1, the voltage characteristics i, 2, 3, a required ateach of the plates of an electrostatic deflection system to produceradial deflection are applied to the deflecting plates D1, D2, D3 andD4. Similarly, as shown in Fig. 2, the currents 6 and I may be suppliedto the deflecting coils M in a magnetic deflection system. For aQQnstant angular velocity, the modulation envelope is sinusoidal and theaverage component is zero. For a stationary trace 5 at any position,such as indicated by the angle or, the average component has a finitevalue and a polarity depending on the value of a, as shown by the dashedcurves.

For any radial trace other than one rotating at a constant velocity theaverage component is not zero. Therefore, conductive coupling or itsequivalent between signal' generating and defleeting systems isessential. A system for radial deflection and variable angularvelocities include ing zero value is thus substantially diflerent inoperation and organization from a system with constant velocity of fieldrotation and diametral deflection. A diametral system termed a radialscanning system in the De Forest Patent 2,241,809, makes no provisionfor transmission of average values other than zero. A circuit for.generating and modulating saw-toothfvoltages as shown in Fig. 1 isillustrated in detail'in Fig. 3. A multivibrator i0 has its outputconnected across a capacitor -9. This circuit is described and claimedin U. S. Patent No. 2,157,434 to James L. Potter. A capacitivevoltagedividerii is also connected across the capacitor 9 and comprisesfour fixed capacitors l3, l5, l1 and i9 and a variable capa-citor 2|.The rotor of the capacitor 2| is mechanically connected to the shaft'(not shown) with which the radial trace is to be synchronized. Theplates of the capacitor 2| are put of an amplifier tube 25, and thecapacitor l3,

connected to the opposite stator plate of the capacitor 2 I, is coupledthrough a polarity reversing tube 21 to the input of an amplifier tube29 The The capacitors l and I9, which are connected to the other pair ofoppositely disposed stator plates of the capacitor 2|, are coupledsimilarly to a pair ofamplifiers with a common load circuit. Thesecircuits are omitted from the drawing for clarity. I

Tile plate circuit 3| is coupled to the grid of a power amplifier tube'33 through a capacitor 35. The plate circuit of the tube 33 includesone pair of the deflecting coils M of a cathode ray tube.Resistors'3land 39 and a screen grid tube 4| are "tubes and 29 have acommon plate circuit 3|.

also included in the plate circuit of the tube 33 and are connected toprovide a constant current 43 through the deflecting coils M to cancelthe zero-signal component 35 of the plate current of: the tube 33. Anauxiliary circuit including tubes 41 and 49 is connected to thegrid ofthe power tube 33 in order to restore the direct current component ofthe signal lost in the capacitively coupled amplifiers 25, 21 and 29.

The operation is as follows: The multivibrator IO produces a sawtoothshaped voltage wave 8 on the capac tor 9. The sawtooth frequency iscontrolled by the circuit constants of themultivibrator and may besynchronized with a signal applied to the input 5|. The voltage 8 isapplied to the capacitive voltage divider ll, resulting voltages l4, I6,l8 and 20 on the corresponding capacitors. The voltage i8 is amplifiedby the tube 25, and the voltage l4, which has a sinusoidal envelopecomponent 180 out of phase with that 'of the voltage 5, is reversed inpolarity by the tube 21, and amplified by the tube 29. The two amplifiedvoltages are combined in the common plate circuit 3 I, cancelling theresidual components caused by the minimum capacitances of the capacitor2| and adding alternately reversed half-sinusolds to produce a voltagewave 32. This is amplified by the power tube 33 to provide a similarlyshaped current wave in the deflecting coils M. In the same manner, thevoltages l6 and 20 across the capacitors l5 and I9 are amplified andcombined to produce a current wave like the voltage 36 in a second pairof deflecting coils, which are spaced 90 around the axis of the cathoderay tube from the first pair.

"Since the voltages 32 and 36 have sinusoidal envelopes-90 out of phase,they will produce the required rotating radial sweep, deflecting thecathode ray beam outward from the center at the sawtooth frequency androtating the resultant radial trace about its inner end at the envelopefrequency, which is 'the frequency of rotation of thevariable capacitor2|. However, this is true onlyif the envelope frequency is high enoughfor. the capacitively coupled amplifiers 25, 21 and-29 to pass itwithout attenuation. When the speed of rotation of the capacitor 2| islower, the voltageacrossthe load-3| assumes the form shown at 34, due tothe fact that the average component, shown by the dashed line, is of toolow a frequency to be transmitted. If the voltage 34 and thecorresponding quadrature voltage 33 were applied to the power amplifierand deflecting circuit, each trace of the cathode ray would have itscenter at the center of the pattern, instead of starting at the center.As the capacitor 2| is rotated slowly, the trace would rotate about itscenter instead of around one of its ends.

The D.-C. insertion circuit, or "clamping circuit operates to restorethe lost average component of the modulated sawtooth wave. The grid ofthe power tube 33 is connected through a pair of diodes 46 and 48 and atapped resistor 53 to a bias source 55. A tube 49 is provided with plateand cathode load resistors 51 and 53, re-

spectively, coupled through capacitors BI and 83,

respectively, to the diodes 46 and 48, which are connected to conduct inopposite directions. The grid of the tube 49 is coupled to receiveimpulses 65 from the multivibrator l0 during the return period of thesawtooth wave. This signal results in .a positive pulse at the cathodeand a negative pulse at the plate of the tube 43, causing both diodes 46and 48 to conduct, momentarily presenting a relatively low impedancepath from the grid of the tube 33 to the resistor 53 and thence to thebias source 55 which is adjusted to provide the proper grid voltage forthe tube 33 at the start of the sawtooth voltage. The tap on theresistor 53 is adjusted to form abalanced bridge circuit with theimpedances of the diodes 48 and 48, preventing the pulses 65 fromreaching the grid of the tube 33. During the pulse time of pulses 35,

corresponding to the sawtooth return period, the coupling capacitor 35is discharged rapidly to the potential existing at that time betweenD.-C. voltage 55 and the plate of the preceding stage. The capacitor 35maintains this potential for one sawtooth period during which the diodes46' and 48 are non-conducting and act as open circuits, and is thenreset again in the same manner, thus causing all sawtooth cycles tobegin with the same voltage, that of the source 55. The signal at thegrid of the tube 33 is hence undistorted as compared with the voltage 32although the amplifier coupling networks do not pass low or zerofrequencies, but only the frequencies needed for transmission of thesawtooth wave 8. AIM- ther advantage in the use of a clamping circuit isthe elimination of extraneous low frequency pickup voltages, such as 60cycle hum which may occur in th grid circuits of the tubes 25 and 21.

For symmetrical electrostatic deflection circuits, four voltages areneeded as shown in Fig. l; the voltages 2 and 4 are obtained byinverting the phase of the voltages and 3 respectively in a conventionalphase inverter circuit. This may be done before the clamping, to allowcapacitive coupling 0! the phase inverters. Each deflection plate of thecathode ray tube is then directly coupled to one power amplifier tubehaving a clamping circuit in its grid circuit.

The deflection circuits can be simplified by combining the halves ofeach sinusoidal modulation envelope after D.-C. restoration. Thevoltages appearing at the respective output terminals of a capacitivevoltage divider connected to a sawtooth wave source as in Fig. 3 areillustrated in Figs. 5a, 5b, 5c and 5d. Upon passing throughcapacitively coupled amplifiers, the direct components of these voltagesare lost, resulting in the waves shown in Figs. 5e 5]. 50 and 5h,respectively. The sawtooth components are in phase in the waves 5e and5!, which represent the two halves of one sinusoidally modulateddeflection voltage, and in the waves 5g and 5h, which represent theother deflection voltage, modulated in quadrature phase with the first.Referring to Fig. 6, a circuit for one of the phases for a single plateof the "electrostatic deflection system is shown. The voltagescorresponding to one phase, for example those of Figs. 5e and 5f, areapplied to the terminals 62 and 54, respectively. The polarity of thesawtooth component of the wave 5f is reversed by a phase inverter 65 andapplied to an output tube 61, while the wave 5c is applied directly toan output tube 69. Diodes H and 13 are connected in the grid circuits ofthe tubes 61 and 69, and act as peak rectifiers, producing D.-C.voltages which are proportional to the average components of thesawtooth waves and are added to them, thus restoring the wave envelopesto the shapes shown in Figs. 5a and 5b. These are combined in the commonplate circuit of the tubes 61 and 69, resulting in a voltage wave likethat shown in Fig. 1a, which is applied directly to a deflection plateof a cathode ray tube 11. The other deflection plate 19 is supplied witha voltage similarly derived from the waves 5g and 5h.

.Fig. 8 shows a circuit for one of the two phase connections for apush-pull or symmetrical electrostatic deflection system. The half wavecomponents, such as those shown in Figs. 5c and 5,, are applied to theterminals 8! and 83, which are connected to the grids of a pair ofamplifier tubes 85 and 81, respectively. The plates of the tubes 85 and81 are coupled to the grids of a pair of power amplifier tubes 89 and9I, respectively, whose plates are connected to one pair of deflectingplates 93 and 95 of a cathode ray tube 91. The power tubes 89 and 9!have a common cathode resistor 99, which is relatively high inresistance as compared to the reciprocal of the transconductance of thetubes 89 and 9| so as to produce phase inversion by cathode coupling. Apair of diodes IM and I03 are connected as peak rectifiers in the gridcircuits of the power tubes, and function like. the diodes II and 13 inthe circuit of Fig. 6. Since the diodes are not 100 percent efficient,they do not supply quite enough D.-C. voltage to restore the averagevalue of the sawtooth waves, and the deflections of the beam in the tube91 tend to start slightly off center. This is compensated by reducingthe A.-C. components by the same percentage. A tap I05 on each of theload resistors I01 of the amplifiers 85 and 81 is coupled through acapacitor I09 to the power tube grid circuit. Resistors III are providedfor isolating this circuit from the peak rectifiers I III and I03, sothat the A.-C. voltage drops on the resistors II I will be subtractedfrom the A.-C. voltages across the rectifiers.

Circuits for magnetic deflection in which alternate half wave signalsare combined after ampower factor. This condition is secured by makingthe reactance of the transformers H1 and I I9 large in comparison to thetotal resistance in the circuit, including the diode resistance. Becauseof this reactance, the diodes become conducting at the start of thesawtooth cycle, maintaining a closed circuit for substantially theentire cycle. This action is similar to that of a half wave rectifiercircuit of low resistance connected to a sine wave generator asillustrated in Fig. 4a. Figs. 4b and 40 show graphic constructions ofthe transient operation of such a circuit under high and low powerfactor conditi'ons respectively. The wave forms e and 2' would beobtained if the diode were short-circuited. The transient voltages tarising when the diode starts to conduct (when e=0) are addedgraphically. When t=e, at the time s, the diode stops conducting. Whenthe power factor is zero, the conduction time is one full cycle, andwhen the power factor is unity, the conduction time is one-half cycle.The current in a low power factor circuit with a diode is henceunidirectional, but'of substantially. the same wave form as without thediode. The D.-C. polarity depends on the polarity of the diode. Thisaction is used in the circuit of Fig. '7 to restore the D.- C. componentof the unidirectional deflection current, producing deflection positionsshown in Figs. 4d and 4e by the traces I21 and I29 with respect to thecenter of a cathode ray tube I3I.

A choke coupled, so called direct drive circuit is shown in Fig. 9. Itsoperation is similar to that of the circuit of Fig. 7. A pair of powertubes II3 and H5 are coupled to the deflecting coils I by means ofchokes I33 and I35 and capacitors I31. The tubes ated class A, and theinput to the tube H5 is reversed in phase by an inverter I39.

Practical sawtooth deflection circuits, particularly when operated atlow frequencies, may cause distortion of the current wave form becauseof insuflicient reactance, resulting in a rapidly decaying wave form asillustrated in Fig. 12a. This is corrected by distorting the drivingvoltage by an equivalent amount as shown in Fig. 12b. This correctionmay be obtained automatically by the use of inverse'feedback. Thevoltage drops on resistors IM and I43 are taken oil on leads I85 and I41and added to the sawtooth signal in the proper polarities in earlierstages of the amplifier pliflcation and D.C. restoration are shown inFig. 7. Referring to Fig. 7, a pair of power amplifier tubes II 3 and H5are arranged to have voltage waves like those shown in Figs. 5c and 5applied to their respective control grids, and their plate circuitsinclude the primaries of a pair of transformers H1 and H9, respectively.The transformer secondaries are connected through diodes l2l and I23 toone pair of deflection coils I25, so that current will flow in only onedirection in one branch circuit and only in the opposite direction inthe other. The deflection coil circuit has a high inductive reactanceand low system.

The circuit shown in Fig. 10 is arranged to permit operation withdifierent ratios of current transformation for e'flicient operation withwidely different sawtooth slopes as shown in Figs, 13a, 13b and 130. Thehigh slope, short duration sawtooth I30 limits the permissibleinductance of the deflection coils I53 to a relatively low value,because the inductive voltage is limited by the available plate supplyvoltage, thus requiring a high current for a given deflection. Theaverage plate current and power dissipation of the tube I5I is, however,moderate because of the long zero current time interval betweendeflection time repetitions. nal no step down is used, and a switch I55is operated to contact point I51, connecting the de-, flection circuitto the primary of the transformer I49. For slower deflection rates, theinductive voltage di a H3 and H5 are oper-.

For this sighas a lower value, permittirrgthe use of a step down ratioand requiring thus a lower peak plate current from the power tube for agiven deflection. In this manner, the total voltage drop reflectedintothe plate circuit of the power tube can be given the same value fordifferent sawtooth slopes, with the power tube operating at maximumefficiency.

Thus far the invention has been described only with reference to the useof modulated sawtooth deflecting voltages. However, it is feasible touse modulated voltages of other shapes, for example, sinusoidal. Theradial velocity of the trace will vary with its radius, instead of beingconstant, as with a sawtooth signal. A circuit adapted for use withmodulated sinusoidal deflection signals is shown in Fig. 11. A source ofsine wave voltage, not shown, is connected across a capacitive voltagedivider like the voltage divider II in Fig. 3. The four output terminalsare connected to the grids of amplifier tubes I59, IGI, I63 and I65,respectively. The plate circuits of these tubes include the primaries ofstep-up transformers I61, I69, Ill and I13, which are tuned to resonateat the oscillator frequency. The transformer secondaries are connectedto rectiflers I15, I11, I19 and IBI which produce the modulationenvelope voltages on their respective loads, which are seriallyconnected for each phase as shown to obtainthe complete summation wavesfor rotation of the cathode ray beam. Radial modulation voltages areobtained directly from the transformers, which are connected in pairswith primaries in opposite polarities and with secondaries in the samepolarities and in series. The radial deflection voltages are coupledover capacitorsv I83 and I85 into the deflection circuits'of the tubeI81. Isolating impedances I89 and I9I prevent these voltages from beingshort circuited by the rectifier filter capacitors I93. Variation of thecapacitors I83 and I 85. allows variation of the radial deflectionamplitude.

Thus the invention has been described as a device for causing a radialdeflection of the beam of a cathode ray tube in a directioncorresponding to the angular position of a shaft, the direction of saiddeflection being unique for each position of the shaft even at low orzero speeds of rotation. The required deflecting voltages are derived bymodulating the output of a. sawtooth or a sine wave generator with acapacitive voltage divider-to produce component waves which arecombined, amplified, and applied to the defleeting circuits. Directcurrent components which are lost in the amplifier and combiningcircuits are restored by a clamping or D.-C. insertion circuit.

I claim as my invention:

1. A deflection system for cathode ray tubes including a deflectionvoltage generator and a plurality of variable voltage dividers connectedacross the output circuit of said generator, a

shaft for driving said voltage dividers, said voltage dividers being soconstructed and arranged that the proportions of the output voltage ofsaid ages and to add said unidirectional voltages to the respectivedistorted voltages from which they are derived.

2. A deflection system for cathode ray tubes including a deflectionvoltage generator and a plurality of variable'voltage dividers connectedacross the output circuit of said generator, a shaft connected to saidvoltage dividers, said voltage dividers being so constructed andarranged that the proportions of the output voltage appearing across theoutput terminals of said voltage dividers are uniquely related to theangular position of said shaft, means for combining said voltagesappearing at the output terminals of one ,pair of said voltage dividersto produce a voltage synchronous with and similar in wave shape to thatproduced by said deflection voltage generator but having. an amplitudeproportional to the cosine of the angle of position f said shaft, andmeans for combining the voltages appearing at the output terminals of asecond pair of said voltage dividers to produce a second voltagesynchronous with and similar in wave shape to that produced by saiddeflection voltage generator but having an amplitude proportional to thesine of the angle of position of said control shaft, means foramplifying said cosine proportional and sine proportional voltagesincluding networks which discriminate against the low frequency anddirect current components of said voltages, means for compensating saiddiscrimination including switching devices arranged to cause each cycleof said disproportionately amplified voltages to form a predeterminedvoltage level, and means for applying said. voltages to respectiverectangularly related deflection elements of a cathode ray tube.

3. A deflection system for cathode ray tubes generator appearing acrossthe output terminals and means for compensating said discriminationincluding rectifiers arranged to derive unidirectional voltagesproportional to the average components of said disproportionatelyamplified voltplurality of voltage dividers connected across the outputcircuit of said generator, each of said voltage dividers comprising avariable capacitor connected in series with a fixed capacitor, a shaftconnected to said variable capacitors, said variable capacitors being soconstructed and arranged that the proportions of the output voltage ofsaid generator appearing across the output terminals of said voltagedividers are uniquely related to the angular position of said shaft,means for amplifying said voltages including coupling networks whichdiscriminate against the low frequency and direct current components ofsaid voltages, and means for compensating said discrimination includingrectiflers arranged to derive unidirectional voltages.

proportional to the average components of said disproportionatelyamplified voltages and to add said unidirectional voltages to therespective distorted voltages from which they are derived.

4. A deflection system for cathode ray tubes including a deflectionvoltage generator and a plurality of voltage dividers-connected acrossthe output circuit of said generator, each of said voltage dividerscomprising a variable capacitor connected in series with a flxedcapacitor, a shaft connected to said variable capacitors, said variablecapacitors being so constructed and arranged that the proportions of theoutput voltage of said generator appearing across the output terminalsof said voltage dividers are uniquely related to the angular position ofsaid shaft, means for amplifying said voltages including couplingnetworks which discriminate against the low frequency and direct currentcomponents discrimination including rectiflers arranged to deriveunidirectional voltages proportional to the average components of saiddisproportionately amplified voltages and to add said unidirectionalvoltages to the respective distorted voltages from which they arederived, and means for compensating the losses in said rectifiers byproviding corresponding attenuation of said distorted voltages.

5.. The invention as set forth in claim 1 wherein said last named meanscomprises diode rectifiers provided with low power factor load circuits.

6. A deflection system for cathode ray tubes including a deflectionvoltage generator and a plurality of variable voltage dividers connectedacross the output circuit of said generator, a shaft connected to saidvoltage dividers, said voltage dividers being so constructed andarranged that the proportions of the output voltage of said generatorappearing across the output terminals of-said voltage dividers areuniquely related to the angular position of said shaft, means foramplifying said latter voltages including networks which discriminateagainst the low frequency and direct current components of saidvoltages, means for compensating said discrimination includingrectifiers arranged to derive unidirectional voltages proportional tothe average components of said disproportionately amplifled voltages andto add said unidirectional voltages to the respective distorted voltagesfrom which they are derived, and means for combining said amplifiedwaves to produce voltage waves synchronous with and similar in shape 'tothat produced by said deflection voltage generator but having amplitudesproportional respectively to the cosine and to the sine of the angle ofposition of said control shaft, and means for applying said resultantvoltages to corresponding deflection circuits of the rectangularlyrelated deflection elements of a cathode ray tube.

'7. The invention as set forth in claim 1 wherein said deflectionvoltage generator produces an amplitude of substantially sinusoidal waveform.

8. The invention as set forth in claim 1 Wherein said amplifier meansincludes resonant circuits tuned to the repetition frequency of saiddeflection voltage generator.

OTTO H. SCHADE.

